'Mrs. Gren' refers to who/what?

'Mrs. Gren' is an acronym for remembering the seven processes of life. All living organisms have these processes in common.

M = Movement. All living things have some degree of self-powered movement, either their entire body or only certain parts. Even plants move: For example, the flower head of a young sunflower follows the arc of the sun as it moves across the sky.

R = Respiration. Respiration is the process by which living things get energy from food. In humans, sugar is broken down for energy with the use of oxygen which creates carbon dioxide as a byproduct.

S = Sensitivity. If a thing is sensitive, then it means that it is able to detect changes to its surroundings. All living things are sensitive: such as barnacles, that close their shells during low tide to prevent themselves from drying out.

G = Growth. All living things grow. Single-celled organisms grow by dividing and making more cells like themselves whereas multi-celled organisms grow by making more cells.

R = Reproduction. Reproduction is the creation of more living things of the same type. For single-celled organisms, the process of reproduction is the same as growing, but for multi-celled organisms, it is more complex.

E = Excretion. All living things produce waste products that need to be removed from them. In single-celled organisms, waste is discharged through the surface of the cell.

N = Nutrition. In order for a living thing to survive, grow and reproduce it needs food and nutrients.